Sodium chloride (salt, NaCl) is essential for human growth and survival. Estimates of the minimum daily intake of sodium that is necessary for growth range from 0.1 to 0.5 g (0.254 g to 1.27 g salt) (Frahk, R. L. and Mickelsen, O. "Sodium--potassium chloride mixtures as table salt." Amer. J. Clin. Nutr. 4:467-470, 1969; Subcommittee on the Tenth Edition of the RDA's--Food and Nutrition Board National Research Council, Recommended Dietary Allowances. 10th ed., Washington, D.C.: National Academy Press, 1989) . An intake of 0.5 g of sodium per day can compensate for urinary, fecal and dermal losses in adults, allowing for wide variations in physical activity and climate. (Subcommittee on the Tenth Edition of the RDA's--Food and Nutrition Board National Research Council, Recommended Dietary Allowances. 10th ed., Washington, D.C.: National Academy Press, 1989). This relatively low requirement for salt is largely the result of strong evolutionary physiological mechanisms developed by most mammals for sodium conservation.
Sodium in the diet is derived from a number of sources. Sodium occurs naturally in foods. It is added to food during processing (non-discretionary use), and is added at the table (discretionary use). In the current Western diet, sodium occurring naturally in foods only contributes about 10% of dietary sodium, while that added during processing contributes up to 75%. Discretionary sodium adds the remaining 15%. (Sanchez-Castillo, C. P., Warrender, S., Whitehead, T. D. and James, W. P. I. "An assessment of the sources of dietary salt in a British population." Clin. Science 72:95-102, 1987). Additional dietary sodium comes from drinking water, water softeners and drugs (i.e., antacids). (Fregley, M. J. "Sodium and potassium." Ann. Rev. Nutr. 1:69-93, 1981).